In general, a detergent is used for removing soils from fabrics, dishes, human bodies, and other articles. Hence, it is very important to ensure mildness of such detergents to the skin in the fields of all household goods, as detergents is to be in direct contact with the human body.
Therefore, many researches have been achieved to develop detergents having improved mildness in the related art. For example, there has been an effort to develop a surfactant having high biodegradability and mildness. As the detergent is based on surfactants in nature, development for an excellent surfactant results directly to a high-quality detergent. As a result of such researches, surfactants for improving biodegradability and mildness have been developed from alkylbenzene sulfonate (ABS), and particular examples thereof include linear alkylbenzene sulfonate (LAS), alpha-olefin sulfonate (AOS), alkyl ethoxylated sulfate (AES), or the like. More recently, alkyl polyglucoside (APG) as a sugar derivative has been developed. Additionally, in order to narrow the distribution of ethylene oxide (EO) addition mole numbers in nonionic surfactants, research and development for converting BRE (broad range ethoxylate) into NRE (narrow range ethoxylate) have been made. In general, as the proportion of a surfactant having a lower EO addition mole number increases in a nonionic surfactant, a detergent becomes have poor quality and becomes highly irritative. Therefore, the NRE technique is designed to reduce the proportion of ethoxylate having a low addition mole number of EO in the total surfactant composition.
In the result of past attempts, it was possible to improve the biodegradability and mildness of a surfactant compared with known surfactants. However, consumers might not be satisfied with such improvements. As past researches focused mainly on the improvement of biodegradability of a surfactant, mildness of a surfactant is hardly improved compared with known surfactants. Additionally, the developed surfactants are not cost-efficient.
It is generally accepted that the detergency and skin mildness (or softness) are contradictory properties of surfactant. Increased detergency is achieved by increasing the emulsifying efficiency, permeating activity and/or foam stability of a surfactant. However, increased detergency also results in the increased removal of protective component of skin and fabrics, along with contaminants. Such inconsistency between the detergency and skin mildness of surfactant is commonly applied to all types of detergents for household goods.
Recently, research and development for so-called softergent has been made intensively in order to have excellent detergency as well as excellent softening effect. However, such softergents are still unsatisfactory due to the aforementioned inconsistency between detergency and mildness. Therefore, many researches have been made since 1970's to solve the above problems and to develop a excellent quality softergent.
Japanese Patent Publication No. Sho56-21795, Japanese Patent Application No. Sho53-53478 and U.S. Pat. No. 4,961,866 disclose detergents using clay, such as bentonite, montmorillonite, or the like, as a softening ingredient. Such detergents had been developed from 1970's to early 1990's. The detergents are characterized by showing an improved softening effect by the accumulation of the clay on fabrics, while not adversely affecting the detergency. However, the detergents still have a poor softening effect comparing to the detergents using a separate fabric softener.
U.S. Pat. No. 5,863,887 discloses a detergent using a tertiary amine as a softening ingredient, instead of a cationic surfactant that interacts with an anionic surfactant, so as to prevent reduction of detergency.
Meanwhile, Japanese Patent Publication No. Hei7-286195 and U.S. Pat. No. 4,141,841 disclose a detergent that uses a cationic surfactant as a softening ingredient and further uses a non-ionic surfactant alone as a cleaning ingredient so as to prevent reduction of detergency, caused by the interaction between the cationic and anionic surfactant, and a detergent that minimizes detergency reduction by inhibiting the dispersibility of the cationic surfactants.
More recently, Japanese Patent Publication Nos. 2001-48851 and 2002-60789 and U.S. Pat. No. 4,095,946 disclose cationic softening ingredients modified from a known cationic surfactants, and particular examples of the modified softening ingredients include alkyldiammonium type, gemini type and polymer type surfactants. Such modified surfactants are characterized in that they do not reduce detergency and show an improved softening effect by virtue of their modified structures, as compared with known quaternary ammonium type cationic surfactants.
As described above, studies that have been made up to date focus on the minimization of the reduction of detergency of a detergent, caused by the mechanism of detergency/softening effect. However, it was not possible to solve the problem fundamentally.